The invention relates generally to lower units of marine propulsion outboard engines, and more particularly, to skegs for such lower units.
High performance outboard engines, such as the 225 horsepower V6 Evinrude(copyright) outboard engine commercially available from Outboard Marine Corporation, Waukegan, Ill., can be utilized in combination with boats capable of traveling at speeds in excess of about 85 m.p.h. Maintaining engine power and control at such high speeds is important for both performance and safety.
To achieve such high speeds, the engine is mounted to the boat so that only a small portion of the engine actually travels in the water. Particularly, only a portion of the engine propeller and lower unit remain in the water at high speeds. A lowermost section of the engine lower unit typically is referred to as a skeg. The skeg extends downwardly from a gear case, and at high speeds, normally all of the skeg remains in the water.
At high speeds, significant torque can be imposed on the engine due to rotation of the propeller, and such torque can adversely affect the steerability of the engine. It would be desirable, of course, to provide a skeg configuration which reduces such torque on of the engine, particularly, at high speeds.
In addition, and at high speeds with some known gear case configurations, blow-out may occur. Blow-out refers to a condition in which cavitation, or a bubble, forms in the water around the bullet and skeg. Specifically, the engine exhaust gases and surface ventilation, at high speeds, cause the bubble to form in the water at the bullet and skeg. When blow-out occurs, engine control and performance are severely affected since the skeg and propeller are engulfed in an air pocket.
Known skeg structures for counteracting steering torque adversely affect engine performance. For example, one known structure includes a separate fin that attaches to one side of the skeg at the skeg aft end. Other known structures include a fin also located at one side of the skeg aft end, but cast integral with the skeg. While such fins may enhance directional control of the engine at high speed, such fins adversely affect engine performance. Particularly, the fins create a drag which results in lower speeds. In addition, the fins are thin and susceptible to being chipped or broken.
Until now, enhancing high speed engine control has been a trade-off to achieving higher speeds. For example, with known skegs including fins, a boat speed penalty occurs. It would be desirable to provide a skeg configuration which not only enhances control at high speeds, but also does not adversely affect engine performance to enable boat speeds of 85 m.p.h. and greater.
These and other objects may be attained by an airfoil shaped skeg which facilitates maintaining engine control even at high speed but does not adversely affect engine performance. In one embodiment, the skeg includes a fore end, an aft end, and opposing sidewalls extend from the fore and aft ends. One sidewall includes a camber, or curved surface. The camber extends from the fore end to the aft end of the skeg. The other sidewall is relatively flat as compared to the cambered sidewall.
In operation, and due to the airfoil shape of the skeg, the skeg does not create any significant extra drag. In addition, the cambered airfoil shape of the skeg counteracts the steering torque generated by rotation of the propeller and enhances the steerability, or control, of the engine.
The above described skeg provide numerous advantages over known high performance skegs in that the present skeg enhances engine control at high speeds yet does not cause any significant speed loss. As explained above, known high performance skegs result in a trade-off between control and performance. In addition, the present skeg is sturdy.